#include<vector>
using namespace std;
int peakIndexInMountainArray(vector<int>& arr) {
    int left = 1, right = arr.size() - 1;
    while (left < right)
    {
        int mid = left + (right - left + 1) / 2;
        if (arr[mid] > arr[mid - 1]) left = mid;
        else right = mid - 1;
    }
    return left;
}